The dispersion of nanoparticles into liquid crystals (LCs) has been performed as a method to enhance the properties of LCs and produce new functional materials. It has been found that as the particle size reaches to the nanometer scale, (10−7-10−9 m.), wherein they are close to the size of LC molecules, the surface anchoring induced elastic distortion of the particles is diminished. At this point, the particle's intrinsic properties become more influential in determining the properties of the LC nanocolloids. Various nanoparticles of different types have been attempted, including metal, fullerene, carbon nanotube, inorganic MgO or SiO, ferromagnetic and others. The formation of dispersions using such materials in conjunction with LCs can provide various features to the LC hosts.
In an example, dispersions of ferroelectric nanoparticles have been produced, with the nanoparticles having enormous dielectric constants in their single crystals. By dispersing low concentrations of ferroelectric nanoparticles into LCs, there has been formed ferroelectric nanocolloidal liquid crystals (FNCLCs) which exhibit significantly enhanced dielectric, and optical properties, such as for LC displays or other applications. Because these types of nanoparticles produce no defects the particles are generally uniformly dispersed in the LC host. The new FNCLCs appear as stable and as homogenous as the pure LC, and may be useful in a variety of applications, replacing conventional liquid crystal formulations.
At the same time, it has been found that the properties of the ferroelectric nanoparticles are extremely sensitive to their preparation techniques and conditions. For example, the techniques in grinding the materials to form the nanoparticles can have an impact on their properties. Further, as with other particle dispersions, coverage of the particles with a surfactant can reduce the particle aggregation and enhance the stability of suspension. Further, with the ferroelectric nanoparticles, a surfactant layer may facilitate maintaining the ferroelectricity of the particles. However, excess surfactant suppresses the order parameter of the liquid crystal and adversely impacts the effect of the ferroelectric particles. Therefore, it is important to precisely control the surfactant concentration during the manufacturing process in order to optimize the properties of ferroelectric liquid crystal colloids.
At present, commercial ferroelectric nanopowders are used as ingredients for making ferroelectric ceramic materials. They are generally pulverized from large crystalline material, and sieved to a nominal size range. Most of these particles lose their ferroelectricity due to strong mechanical collisions in this process during milling. If there is any remaining, their strong dipolar moment can induce severe agglomeration over a μm scale. These powders need to be compounded with binding material and sintered at high temperature (>1000° C.). Usually a high voltage (>kV) poling is performed as a post treatment. These post treatments help to restore the ferroelectricity lost during pulverization process. However, both these treatments are difficult to be realized in association with FNCLCs, where nanosized particles were mixed with liquid crystals.